1. Field of the Invention
The present invention relates to a gas sensor having a detecting element having a pair of electrodes formed on a surface of a solid electrolytic body of an oxygen ion conductive property, and measuring the concentration of a measured gas.
2. Description of the Related Art
Various kinds of gas sensors such as an HC sensor, a NOx sensor, etc. are conventionally known as a gas sensor for detecting a concentration of a specific gas component from a mixing gas. An oxygen sensor having a detecting element made by a solid electrolytic body of an oxygen ion conductive property is known as one of these gas sensors.
As shown in FIG. 10, a detecting element 102 of a general oxygen sensor 101 is made such that an inside electrode 102a and an outside electrode 102b are formed on an inner and outer surfaces of a cylindrical body having a bottom. A tip side of the cylindrical body is covered by the solid electrolytic body. A rear end side of the cylindrical body is opened by the solid electrolytic body.
The oxygen sensor 101 detects an oxygen concentration of a measured gas by electromotive force caused between electrodes by a concentration difference between the measured gas outside the detecting element 102 and an atmosphere as a reference gas filling an internal space 102c of the cylindrical body.
In the oxygen sensor 101 for detecting the oxygen concentration of the measured gas by such a principle, the detecting element 102 is held by a metal shell 111 such that the tip portion of the detecting element 102 is exposed to the measured gas from the tip side of a through hole 112 formed in the axial direction of the metal shell
The detecting element is covered with an outer sleeve 113 so as to protect the detecting element from dust, water, oil, flied stones, etc. therearound.
In the oxygen sensor 101, a rear end opening portion of the outer sleeve 113 is covered by an outer sleeve cover 130 as a seal member manufactured by rubber.
However, in a perfect covering state, no sufficient atmosphere (reference gas) can be sent into the internal space 102c of the detecting element 102 stored into the oxygen sensor 101. Accordingly, it is known that a vent hole 131 is arranged in the outer sleeve cover 130 of the oxygen sensor 101 of this kind.
A filter 153 has a permeable property and a water repellent property to selectively introduce the atmosphere into the outer sleeve 113 while preventing the invasion of water into the outer sleeve 113. The filter 153 is arranged in this vent hole 131 so as to block the vent hole 131 (e.g., see patent literatures 1 and 2).
[Patent Literature 1]
JP-A-2000-193632 (see FIG. 3)
[Patent Literature 2]
JP-A-2001-208724 (see FIG. 1)
In the oxygen sensors described in the above patent literatures, a vent hole is covered by a filter by fixing the filter using another member such that the filter comes in contact with an entire inner face of the vent hole. Therefore, there are cases in which manufacture cost of the sensor is raised and the filter is damaged in a manufacture process of the sensor.
Namely, in the oxygen sensors described in the above patent literatures, as shown in FIG. 11, a sleeve-shaped insertion member 151 is covered with a sheet-shaped filter 153, and this filter 153 is pushed into the vent hole 131 from forward (the side of a metal shell).
Thus, the vent hole 131 is covered by the filter 153 while the filter 153 comes in contact with the inner face of the vent hole 131. Therefore, in the pushing process of the insertion member 151 into the vent hole 131, there is a case in which the filter 153 is pulled in the direction opposed to the insertion direction so that the filter 153 is broken.
When the vent hole 131 is covered by the filter 153 in such a method, the filter 153 is arranged outside the insertion member 151, and is fixedly nipped and supported between the inner face of the vent hole 131 and the outer circumferential face of the insertion member 151 in design. Accordingly, the filter 153 of a size sufficiently greater than the diameter of the vent hole 131 must be prepared. Therefore, manufacture cost is raised and there are many useless portions.
It is an object of the present invention is to provide a gas sensor capable of attaching a filter to a vent hole simply and with a low cost.
To achieve such an object, a gas sensor comprising a detecting element having a pair of electrodes formed on the surface of a solid electrolytic body of an oxygen ion conductive property; a metal shell having a through hole formed in the axial direction and holding the detecting element within the through hole so as to expose the tip portion of the detecting element to a measured gas from the tip side of this through hole; an outer sleeve arranged on the rear end side of the metal shell and internally accommodating the detecting element; and an outer sleeve cover fitted and inserted in a rear end opening portion of this outer sleeve and extended from its own rear end face to the tip face, and having a vent hole as a circulating path of a gas of the interior and the exterior of the outer sleeve. A filter unit formed by a body separated from a gas sensor main body is arranged in the gas sensor.
The filter unit has a tubular member fitted and inserted into the vent hole of the outer sleeve cover, and a filter arranged inside this tubular member and fixed on the inside of this tubular member and having a permeable property and a water repellent property. The filter unit has such that the filter unit is fitted and inserted in the vent hole of the outer sleeve cover and the vent hole is covered by the filter.
In the gas sensor made in this way, the filter unit for fixing the filter inside (interior) the tubular member is used. Accordingly, if this filter unit is fitted and inserted into the vent hole of the outer sleeve cover, the vent hole can be simply covered by the filter. In other words, in the present invention, the gas sensor can be simply made by attaching the filter unit to the vent hole such that a gas can be circulated in the interior and the exterior of the outer sleeve while the invasion of a waterdrop, dust, etc. into the outer sleeve from the vent hole is prevented by the function of the filter. The productivity of a product can be improved in the gas sensor of the present invention.
The conventional gas sensor adopts the method for mounting the filter to the outer sleeve cover so as to set the filter to the exterior of an insertion member and directly push the filter into the vent hole. Therefore, there is a case in which the filter is damaged during the insertion. However, in the present invention, since the filter is mounted to the inside of the tubular member in advance, no filter is damaged when the filter unit is fitted and inserted. Accordingly, in the gas sensor of the present invention, manufacture cost of the product can be restrained and reliability of the filter, therefore, reliability of the gas sensor can be improved.
When the filter unit includes a separate body in this way and the filter unit is simply fitted, inserted and attached to the outer sleeve cover, there is a possibility that the filter unit gets out of the vent hole by vibrating the gas sensor after the attachment. Accordingly, for example, the filter unit is preferably fixed to the outer sleeve cover by an adhesive, etc. so as to prevent the filter unit from getting out of the outer sleeve cover.
However, performance of the adhesive is reduced when time has passed. Therefore, there is a possibility that no filter unit can be firmly fixed to the outer sleeve cover for a long period.
Therefore, in the gas sensor, a first engaging portion engaged with the tip portion (metal shell side) of the outer sleeve cover, and a second engaging portion engaged with the rear end portion (the side opposed to the metal shell) of the outer sleeve cover are preferably arranged in the tubular member.
In the gas sensor, the filter unit is fixed to the outer sleeve cover such that the outer sleeve cover is nipped by the first and second engaging portions from both opening portion sides of the vent hole. Therefore, the extraction of the filter unit can be reliably prevented in comparison with the case using the adhesive, etc.
In particular, the filter may be fixed to the tubular member so as to be arranged on the rear end side from the vent hole of the outer sleeve cover.
In other words, the filter may be fixed to the tubular member to be projecting form the rear end face of the outer sleeve cover. The filter upper face (a face located on the rear end side of the gas sensor) is located on the backward side from the rear end face (a face located on the side opposed to the metal shell) of the outer sleeve cover by arranging the filter on the rear end side from the vent hole of the outer sleeve cover in this way.
Therefore, when the gas sensor is used, it is possible to effectively restrain that water is collected and dust is accumulated on the filter upper face.
However, when the filter is fixed to the tubular member so as to be arranged on the rear end side from the vent hole of the outer sleeve cover, it is possible to restrain water from being collected on the filter upper face, but the danger of damage of the filter due to flied stones is increased. Therefore, the filter may be also fixed to the tubular member so as to be arranged within the vent hole of the outer sleeve cover. The filter upper face is located on the forward side from the rear end face of the outer sleeve cover by arranging the filter within the vent hole of the outer sleeve cover in this way. Therefore, it is possible to effectively prevent flied stones, etc. from hitting against the filter so that the damage of the filter can be effectively restrained.
However, when the filter is arranged within the vent hole of the outer sleeve cover, the damage of the filter due to flied stones, etc. can be restrained, but there is a fear that water, etc. are collected on the filter upper face as mentioned above. Therefore, a construction of of a gas sensor is used for solving both the problem of collecting water, etc. on the filter upper face, and the problem of damaging the filter by flied stones, etc. In this construction, while the construction for fixing the filter to the tubular member so as to be arranged within the vent hole of the outer sleeve cover is set to a premise, a groove portion having one end side communicated with the vent hole and the other end side opened to the side wall face of the outer sleeve cover is formed on the rear end face of the outer sleeve cover, and the filter is arranged on the rear end side from a deepest portion of the groove portion.
Namely, in the gas sensor of the present invention, the damage of the filter due to flied stones, etc. can be prevented since the rear end face of the outer sleeve cover is located in a position higher than that of the filter as mentioned above by arranging the filter within the vent hole of the outer sleeve cover. In addition, in the gas sensor of the present invention, the groove portion having one end side (inside) communicated with the vent hole and the other end side (outside) opened to the side wall face of the outer sleeve cover is formed on the rear end face of the outer sleeve cover, and the filter is arranged on the rear end side from the deepest portion of this groove portion. In other words, the filter is disposed between a deepest portion of the groove portion and the rear end face of the outer sleeve cover.
Accordingly, even when water is splashed on the filter, this water can be discharged to the diametrical outside of the outer sleeve cover through the groove portion located in a position lower that that of the filter. Namely, it is possible to simultaneously solve both the problem of collecting water, etc. on the filter upper face and the problem of damaging the filter by flied stones, etc. by arranging the deepest portion of the above groove portion in a low position while the rear end face of the outer sleeve cover is arranged in a high position with the filter as a reference. The shape of the groove portion is not particularly limited, but can be formed in a U-shape and a V-shape in section.
With respect to the above groove portion, it is preferable that the outer sleeve cover has plural through holes for a lead wire for inserting the lead wire electrically connected to the detecting element, and the plural groove portions are formed on the rear end face of the outer sleeve cover in positions not interfering with the through holes for the lead wire. In other words, the groove portion is formed on the rear end face of the outer sleeve cover except for where the through holes for the lead wire are formed.
Namely, water, etc. splashed on the filter upper face can be efficiently discharged toward the diametrical outside of the outer sleeve cover through the groove portion by forming the groove portion by effectively practically utilizing the limited accumulation of the outer sleeve cover.
A filter also having an oil repellent property is preferably used as the filter.
The filter of a water repellent property is used as the above filter to water-tightly block the vent hole. However, when the oil is attached to the filter of the water repellent property, this water repellent property cannot be sufficiently shown. In consideration of such a problem, the oil repellent property is provided by performing oil repellent processing, etc. in the filter in the gas sensor. In particular, there is a possibility that the gas sensor for a vehicle, etc. is polluted by the oil. Accordingly, if the filter of the oil repellent property is used in the filter unit in this way, performance of the filter unit can be maintained for a long period.
In the gas sensor of the present invention, the filter unit is preferably made such that plural filters are fixed to the inside of the tubular member. If a filter set to be arranged in an outermost layer is broken, waterproof property can be maintained by the other filters by arranging the plural filters inside the tubular member in this way. When the plural filters are arranged inside the tubular member, the plural filters can be overlapped or arranged at a predetermined interval with respect to the central axis direction of the tubular member.
Further, in the gas sensor of the present invention, the filter unit is preferably made such that a partition plate having plural opening portions for exposing the filter is fixed to the rear end side from the filter inside the tubular member. Since the partition plate having the plural opening portions is arranged on the rear end side (in other words, the filter upper face) of the filter in this way, the atmosphere can be introduced into the outer sleeve while the damage of the filter due to flied stones, etc. can be effectively prevented.
In addition to this, a seal member for water-tightly fixing the filter inside the tubular member is preferably arranged within the filter unit to water-tightly hold the interior of the filter unit.
If the filter unit having such a seal member is fitted and inserted into the vent hole of the gas sensor, it is possible to sufficiently restrain that a waterdrop, etc. are invaded into the filter unit through the gap between the filter and the tubular member, and the interior of the outer sleeve is polluted by the waterdrop, etc. As a result, the performance of the gas sensor can be maintained for a long period. The seal member may be an adhesive able to adhere the filter outer edge to the inner wall of the tubular member, and may be also a seal member such as an O-ring manufactured by rubber. In particular, when the seal member manufactured by rubber is used, the rubber is adhered to the inner wall of the tubular member in the application of heat so that it is effective to take an airtight measure within the gas sensor.
If productivity of the filter unit is considered, the gas sensor is preferably made so that a filter fixing portion for fixing the filter in a predetermined position inside the tubular member is arranged in the tubular member. The filter unit is made such that the filter and an O-ring as the seal member are fixedly nipped and supported between the filter fixing portion and an end portion of the tubular member folded in the inside direction of the tubular member.
In the gas sensor of such a construction, the O-ring and the filter are stored to the filter fixing portion formed inside the tubular member so as to be overlapped, and the end portion of the tubular member is then folded by bending processing, etc. in the inside direction of this tubular member so that the filter unit can be completed. Accordingly, the filter unit can be simply and efficiently manufactured.
In the gas sensor, a step portion as the above filter fixing portion is formed in the inner wall of the tubular member by enlarging the tubular member in diameter on a predetermined boundary. The O-ring and the filter are arranged on one end side of the tubular member enlarged in diameter so as to be overlapped with the above step portion, and the O-ring and the filter are stored inside the tubular member.
Further, in the gas sensor, the O-ring and the filter are nipped and supported between the step portion as the filter fixing portion and the end portion of the tubular member by folding the end portion of the tubular member on one end side in the inside direction of the tubular member. Thus, the filter unit is made so as to fix the O-ring and the filter.
When the method for forming the step portion by the diameter enlargement of the tubular member in this way is adopted, the filter fixing portion can be simply formed inside the tubular member.
Further, when the step portion is formed in the tubular member by the diameter enlargement, the first or second engaging portion can be formed in the outer wall of the tubular member corresponding to the step portion. Accordingly, the number of processes at the manufacturing time of the filter unit can be reduced, and productivity of the filter unit can be improved.